It is known that ubenimex (INN) inhibits aminopeptidase B (cf. U.S.P. No. 4,189,604) and has a antitumor activities (cf. Japanese Pat. Publication (A2) No. 9487/1985) as well as a low toxicity. It has already been put into commercial use under a tradename of Bestatin.RTM..
Myelodysplastic syndrome, which will be referred to simply MDS hereinafter, is mainly observed among aged people in high frequently. It causes dysplastic hematopoiesis and refractory to common hematopoietics. It is apt to transform to acute leukemia, or it frequently induces death due to serious infectious diseases, anemia or hemorrhage caused by dysfunction of blood cells. At present no standard therapy is established and several attempts are being made to treat this disease by using some adrenocortical hormones, androgen, hematopoietic vitamins, Ara-C and its derivatives or interferon .gamma.. However, no satisfactory therapeutic effects is obtained with these drugs. Thus it has been desired to develop an more effective remedy for MDS, in particular for high blast types, refractory anemia with excess of blast (RAEB) and RAEB in transformation (RAEB-t).